The present invention relates to a screw used for converting rotational and linear movement through the motions of mutually fitting male and female screw members. In particular, the present invention relates to a thread surface of a screw which is operated with a high relative speed and load. More specifically, the present invention is intended for supporting and adjusting a position of a slide in a machine press.
In general, when a male and female screw members are meshed and rotational and linear motion is converted via the relative motions of the screw members at relative high speeds and loads, wear of the screw members causes damage and ultimately results in the inoperability of the screw members. One method used to reduce wear includes applying a lubricating oil to a clearance area between the meshing sections of the male and female screw members. The lubricating oil prevents wear on the screw surface and also reduces the resistance on the screw thread surface.
Another method used for reducing wear resistance is a ball screw. A ball screw includes a ball interposed between a screw shaft and a nut (female screw member). This results in a rolling contact instead of a sliding contact between the screw members which reduces wear and provides high transfer efficiency.
In the former of the above methods, the lubricating oil between the male screw surface and the female screw surface tends to gradually break down which gradually increases the resistance between male screw and the female screw. As the resistance increases, the rate of wear of the parts increases until the clearance between the meshing sections is no longer adequate for the purpose of the high speed and high load operation. The breakdown of the oil film usually takes place when the load applied to the screw surface is great, making the screw unusable.
In the latter of the above methods, involving rolling contacts, the wear between the screw parts is decreased. However, the area of the interface between the two moving parts is small making the load capacity relatively small. Thus, the ball screw method for reducing wear is not suited for applications involving heavy loads.